1. Field of the Invention
The present invention relates to a hydraulically controlled intake valve for an internal combustion engine.
2. Description of Related Art
Internal combustion engines contain an intake valve and an exhaust valve for each cylinder of the engine. In a compression ignition (CI) engine the intake valve allows air to flow into the combustion chamber and the exhaust valve allows the combusted air/fuel mixture to flow out of the chamber. The timing of the valves must correspond to the motion of the piston and the injection of fuel into the chamber. Conventional CI engines incorporate cams to coordinate the timing of the valves with the piston and the fuel injector. Cams are subject to wear which may affect the timing of the valves. Additionally, cams are not amenable to variations in the valve timing during the operation of the engine.
U.S. Pat. No. 5,125,370 issued to Kawamura; U.S. Pat. No. 4,715,330 issued to Buchl and U.S. Pat. No. 4,715,332 issued to Kreuter disclose intake valves that are controlled by solenoids. Each valve is moved between an open position and a closed position by energizing the solenoids. The amount of power required to actuate the solenoids and move the valves is relatively large. The additional power requirement reduces the energy efficiency of the engine.
U.S. Pat. Nos. 4,200,067 and 4,206,728 issued to Trenne; U.S. Pat. Nos. 5,248,123, 5,022,358 and 4,899,700 issued to Richeson; U.S. Pat. No. 4,791,895 issued to Tittizer; U.S. Pat. No. 5,237,968 issued to Miller et al. and U.S. Pat. No. 5,255,641 issued to Schechter all disclose hydraulically controlled intake valves. The hydraulic fluid is typically controlled by a solenoid control valve. The solenoid valves described and used in the prior art require a constant supply of power to maintain the valves in an actuating position. The continuous consumption of power reduces the energy efficiency of the engine. Additionally, the solenoid control valves of the prior art have been found to be relatively slow thus restricting the accuracy of the valve timing. It would therefore be desirable to provide a camless intake valve that was fast and energy efficient.
The exhaust valve of a internal combustion engine is opened for the exhaust stroke of the engine cycle. Before the exhaust valve is opened, there is a differential pressure across the valve equal to the difference between the pressure of the exhaust gas within the combustion chamber and the pressure within the exhaust manifold. The force required to open the valve must be large enough to overcome this differential pressure. When the valve is initially opened, the exhaust gas flows out of the combustion chamber and rapidly reduces the pressure within the chamber. After the exhaust valve is initially opened, the force that continues to open the valve is generally must larger than the energy required to overcome the gas pressure within the chamber. This additional work ultimately lowers the energy efficiency of the engine. The lost energy can be significant when multiplied by the number of exhaust strokes performed by an engine. It would therefore be desirable to provide an exhaust valve assembly that optimizes the opening force of the valve.